For certain types of minimally invasive medical procedures, endoscopic visualization of the treatment site within the body is unavailable or does not assist the clinician in guiding the needed medical devices to the treatment site.
Examples of such procedures are those used to diagnose and treat supra-ventricular tachycardia (SVT), atrial fibrillation (AF), atrial flutter (AFL) and ventricular tachycardia (VT). SVT, AFL, AF and VT are conditions in the heart which cause abnormal electrical signals to be generated in the endocardial tissue to cause irregular beating of the heart.
A procedure for diagnosing and treating SVT or VT involves measuring the electrical activity of the heart using an electrophysiology catheter introduced into the heart via the patient's vasculature. The catheter carries mapping electrodes which are positioned within the heart and used to measure electrical activity. The position of the catheter within the heart is ascertained using fluoroscopic images. A map of the measured activity is created based on the fluoroscopic images and is shown on a graphical display. A physician uses the map to identify the region of the endocardium which s/he believes to be the source of the abnormal electrical activity. An ablation catheter is then inserted through the patient's vasculature and into the heart where it is used to ablate the region identified by the physician.
To treat atrial fibrillation (AF), an ablation catheter is maneuvered into the right or left atrium where it is used to create elongated ablation lesions in the heart. These lesions are intended to stop the irregular beating of the heart by creating non-conductive barriers between regions of the atria. These barriers halt passage through the heart of the abnormal electrical activity generated by the endocardium. Following the ablation procedure, a mapping catheter is positioned in the heart where it is used to measure the electrical activity within the atria so that the physician may evaluate whether additional lesions are needed to form a sufficient line of block against passage of abnormal currents. S/he may also attempt to induce atrial fibrillation using a pacing electrode, and then further evaluate the line of block by analyzing the time required for the induced electrical activity to pass from one side of the block to the other.
The procedures used to diagnose and treat SVT, VT, AFL and AF utilize catheters which are maneuvered within the heart under fluoroscopy. Because the fluoroscopic image is in two-dimensions and has fairly poor resolution, it may be difficult for the physician to be certain of the catheter positions. Thus, for example, once a physician has identified an area which is to be ablated (using a map of the measured electrical activity of the heart) it may be difficult to navigate an ablation catheter to the appropriate location in order to accurately ablate the area of concern. It is therefore desirable to provide a system by which the positions of medical devices such as mapping and ablation catheters may be accurately guided to selected regions of the body.
U.S. Pat. No. 6,216,027, “SYSTEM FOR ELECTRODE LOCALIZATION USING ULTRASOUND,” assigned to Cardiac Pathways Corporation and incorporated herein by reference, describes a device localization system that uses one or more ultrasound reference catheters to establish a fixed three-dimensional coordinate system within a patient's heart, preferably using principles of triangulation. The coordinate system is represented graphically in three-dimensions on a video monitor and aids the clinician in guiding other medical devices, which also carry ultrasound transducers, through the body to locations at which they are needed to perform clinical procedures. The system is preferably used in the heart to help the physician guide mapping catheters for measuring electrical activity, and ablation catheters for ablating selected regions of cardiac tissue, to desired locations within the heart.
Three-dimensional images are shown on a video display which represent the three-dimensional positions and orientations of the medical devices used with the system, such as the reference catheters, and the electrodes of the mapping catheter and ablation catheter. The video display may additionally include representations (color differences, ispotential or isochronal maps, symbols etc.) of the electrical activity measured by each mapping electrode at its respective location on the three-dimensional display. It may also represent ablation lesions formed within the body at the appropriate three-dimensional locations, and/or certain anatomic structures which may facilitate navigation of the medical device(s) within the patient.
An enhancement to the three-dimensional localization system described above has now been developed. The enhancement improves the graphical display by showing medical devices positioned within the living body superimposed with a three-dimensional graphical representation of the region of interest within the patient's body. The graphical representation of the region of interest is based upon a model of the region of interest programmed into the system software and dynamically updated to conform with the actual region of interest as information concerning actual features of the region of interest is gathered using a probe manipulated within the patient's body.